Cannot read property 'abc' of undefined

[bizeasy17]

environment
nodejs 8.0
express 4
i18n-node 3.0
give the error "Cannot read property 'abc' of undefined" when define the text in .hbs template file

in index.js (middleware)
`var i18n_module = require('i18n-nodejs'),//2018-4-22 JH
....
// 2018-4-22 JH START
var config = {
"lang": "zh-cn",
"langFile": path.join(__dirname + "/../locales/locale.json")//relative path to index.js file of i18n-nodejs module
}
var i18n = new i18n_module(config.lang, config.langFile);

...
module.exports = function(app, db, callback) {
...
app.engine('hbs', hbs.express4({
handlebars: HandleBars,
defaultLayout: path.join(__dirname, '../views/layout/main.hbs'),
i18n: i18n,//2018-4-24 JH
partialsDir: [path.join(__dirname + '/../views/partials/'), path.join(__dirname + '/../views/subviews/reports')]
}));
app.set('view engine', 'hbs');
hbsHelpers.register(hbs.handlebars);
...`

in template
<h4 style="font-size: 24px; margin-top: 7px; font-weight: 300;color: #222;"> {{__ 'PrivacyPolicy'}} <a class="uk-modal-close uk-close no-ajaxy right" aria-label="Close"></a> </h4>

in .json locale file
{ "TruDesk i18n initialized.": { "ar": "مرحبا", "zh-cn": "TruDesk i18n 初始化成功." }, "PrivacyPolicy": { "zh-cn": "隐私政策", "en": "Privacy Policy" } }